1. Field of the Invention
This invention relates to the preparation and use of catalysts comprising a mixture of tungsten oxide and silica supported on a boehmite-like surface. More particularly, this invention relates to the preparation of catalyst supports and cracking catalysts comprising mixtures of tungsten oxide and silica supported on a boehmite-like surface which are prepared by forming a composite of a mixture of (a) tungsten oxide or tungsten oxide precursor, (b) particles of silica and (c) particles of boehmite and subjecting said composite to high temperature steaming at a temperature of at least about 500.degree. C. for a time sufficient for at least a portion of said silica and tungsten oxide mixture to react with the surface of the boehmite as the bulk boehmite converts to alumina.
2. Background of the Disclosure
The use of silica-alumina composites as catalysts and as catalyst support materials is well known to those skilled in the art. These catalysts are prepared in many different ways such as co-precipitation, various co-gel techniques, by contacting alumina with various silica precursor salts such as organosilanes, including alkoxy silanes followed by calcination of the so-formed composite to produce the desired silica-alumina material. Use of the latter techniques enables one to obtain an alumina whose surface is partly or completely covered with silica as opposed to a homogeneous or heterogeneous silica-alumina composite.
U.S. Pat. No. 4,440,872 to Grenoble et al discloses various acid cracking catalysts. Some of the catalyst supports are prepared by impregnating gamma alumina with a silane compound followed by either calcining or steaming the impregnate at 500.degree. C. The calcined support material is then impregnated with ammonium meta-tungstate which is steamed at high temperature to form a catalyst. Peters et al in U.S. Pat. No. 3,671,432 disclose a process for preparing a supported transition metal of Group V or VI of the Periodic Table which includes mixing a water dispersible transition metal compound with particles of support material and calcining the mixture at a temperature of from 200.degree.-1000.degree. C. However, the disclosure contains examples employing only either chromium trioxide or vanadium pentoxide as the water dispersible transition metal compounds. U.S. Pat. No. 3,668,151 mixes particulate zinc oxide with particulate gamma alumina and calcines the mixture at 600.degree.-1500.degree. C. Browning et al in U.S. Pat. No. 3,182,012 prepare a cracking catalyst comprising cobalt and molybdenum on a silica-alumina support. The silica and alumina may be mixed as dry powders, but the cobalt and molybdenum are deposited on the support by impregnation. The final impregnate is calcined at 600.degree.-1200.degree. F.
In U.S. Pat. No. 2,830,960 Broomhead mixes cobalt formate, molybdic and an alumina hydrogel, followed by drying and calcining the mixture at 450.degree.-650.degree. C. Porter et al in U.S. Pat. No. 2,640,802 disclose mixing powdered cobalt oxide, molybdic oxide and alumina, pelleting the mixture and heating the pellets for two hours at 530.degree. C. U.S. Pat. No. 3,151,091 discloses preparing alumina based catalyst by dry mixing alumina with an oxide of a metal selected from the group consisting of the iron transition metals, molybdenum, tungsten, vanadium and mixtures thereof and calcining the resulting mixture at 800.degree.-1200.degree. F.
U.S. Pat. No. 2,394,796 discloses impregnating a porous, hydrated alumina, including boehmite, with silicon tetrachloride or tetraethylsilicate, followed by hydrolysis of the impregnate to form silica. In U.S. Pat. No. 2,493,896 an alumina support material is impregnated with ethylsilicate or a polymer of ethylsilicate, followed by calcination. Multiple impregnations, with calcining after each impregnation, are said to yield a catalyst containing up to 50 wt. % silica. In U.S. Pat. No. 4,172,809 a process for preparing alumina extrudates is disclosed wherein a silicon compound is added to an alumina gel during extrusion of the gel. The resulting extrudate is then calcined. U.S. Pat. No. 2,579,123 discloses reactivating deactivated silica-alumina catalysts by impregnating with a silicon or silicate compound, followed by calcination.
U.S. Pat. No. 3,502,595 discloses the preparation of silica-alumina catalysts by impregnating a hydrated alumina, including boehmite, with one or more organic esters of silicon followed by calcination. U.S. Pat. No. 4,038,337 discloses the preparation of a silica-alumina catalyst by reacting gamma or eta alumina with various esters of orthosilicic acid followed by calcination. U.S. Pat. No. 4,080,284 discloses contacting a support material, such as alumina, with an organic or halogen-substituted silane. The silylated support material is then calcined, followed by steaming at 900.degree.-1600.degree. F.
U.S. Pat. No. 4,013,589 discloses a process for improving the mechanical and thermal properties (stability) of gamma alumina by impregnating the alumina with a hydrolyzable silicone compound and hydrolyzing the impregnate to convert the silicone compound to silica. Temperatures of up to 500.degree. C. are employed for the hydrolyzing step. In one example, a negative comparative example, the alumina was impregnated with a "Ludox" slurry (a solution of colloidal silica) followed by calcination in air at 500.degree. C.